dunham



March 26, 1929. c. A.QDUNHAM METHOD OF HEATING BY SUBATMOSPHERIC STEAM Filed July 15. .1927

4 Sheets-Sheet 1 DDUDD uuquuuuuuuuuuu Dun Du uuuuuuuuuuuuuu l lnf #211151 022 Ail/1250772 Q MAXI; fl orne g uuuuuuuuuruuuuuuuuu uuuuuuuuuuuuuuuuuuu March 26, 1929. g, DUNHAM 1,706,401"

IETHOD 0F HEATING BY SUBATMOSPHERIC' STEAM Filed July 15, 1927 i 4 Sheets-Shed 2 Mara, 26, 1929. C: N AM 1,706,401

METHOD OF HEATING BY SUBATMOSPHERIC STEAM Filed Jul? 15, 1927 I 4 Sheets-Sheet 3 March 26, 1929. c. A. DUNHAM METHOD OF HEATING B! SUBA'I MOSPHERIC STEAM 4 sheets-sheet" 4 Filed July 15, 1927 Infant); [7a [522 Ajzmzam irms Patented Mar. 26, 1929.

UNITED STATES 1,706,401 PATENT OFFICE,

CLAYTON a. DUNHAM, on GLENGOE, ILLINOIS, ASSIGNOR To C. ntrNHn u COMPANY, or MARSHALLTQWN, IOWA, A CORPORATION on owa.

METHOD OF HEATING BY SUBATMOSPHERIC STE-AM.

Application filed July 15,

This invention relates to a new method of heating by means 01' a multiple-unit vacuum heating system. Such a method is particu larly adapted for use in very large buildings, wherein different sections of the building are simultaneously subject to different temperature conditions due to different locations in the building, different distances from the source of steam supply, different exposures, differences in building construction, or other conditions, so that there are different heating requirements in these different building sections.

This method is an adaptation to the requirements noted hereinabove of the differential vacuum steam heating system disclosed and claimed in my copending application Serial No. 171,616, filed Feb. 28, 1927, now Patent No. 1,644,114, grantedoctober 4, 1927. Such a system includes a steam generator or other source of supply, from whichsteam 1s supplied to the radiators at an adjustable subatmospheric pressure. A thermostatically operated trap at the outlet of each radiator normally prevents the escape of steam, but permits the escape of accumulated liquid condensates and air to a return main leading down to an accumulator tank. Suitable 'vacuum-producing means serves to withdraw this liquid condensate and air, vent the air, return the water tothe steam generator, and maintain the necessary vacuum in the return main and also throughout the system! By means ofa suitablereducing valve in the s o f pipe, the sub-atmospheric pressureot the ste: m delivered to the radiators may be varied. in accordance with the heat output desired to meet the temperature requirements. Dual control means is provided for the vacuumproducing mechanism whereby it is automatically operated to maintain a substant-ially constant difference in pressure he tween the supply and return sides of the system, regardless of the absolute pressure maintained in the supply main, and is also operated in accordance with the level of the accumulated liquid condensate inorder to return this water to the steam generator.

According to the present invention, in its preferred embodiment, each separate section of the building is provided With a differential vacuum heating system of the type just briefly described. A single generator or group of boilersis provided for supplying the steam to the seve al separate distributing systems,

1927. Serial No. 205,978.

and the reducing valves for all of the systems are grouped or centralized adjacent suitable temperature indicating instruments connected with certain key-rooms in each of the sections of the building. These instruments indicate the dilierent sin'iultaneous temperature requirements in the different building sections, and in accordance with these indications the operator may suitably adjust the different reducing valves so that the subatmospheric pressure of the steam supplied to each unit or branch of the system will correspond to the heating requirement in that building section. The returns from the several distributing systems are led'back to a group of separate vacuum-producing mechanisms, all of which discharge their accumulated liquid condensates back to the common source of steam supply.

The principal object of this invention is to provide a new method and ap aratus for heating large buildings, such as has been briefly described liereinaboveflnd is disclosed more in detail in the description which follows.

Another object is to provide means whereby an auxiliary pressure-control unit may be temporarily substituted for any one of the similar units normally used in the several distributing systems.

Another object is to provide means Whereby an auxiliary vacuun'i-producing mocha nisin may be substituted for the similar mechanism normally used in each of the systems.

Another object is to provide means whereby exhaust steam from an engine or other source may be distributed at the proper subatmospheric pressure to any one or a'll of the several distinct distributing systems.

Other objects and advantages of this invention will be more apparent from the following detailed description of one approved form of apparatus suitable for carrying out the principles of this invention.

In the accompanying drawings:

Fig. 1 is diagrammatic illustration of a large office-building, wherein this improved heating system might be advantageously used.

Fig. 2 illustrates the essential parts of any one distributing unitof the heating system.

Fig. 3 is a plan view of the centralized supply and return port-ions of the heating system.

Fig; 4.- is a vertical section through the boiler-room and adjacent portions of the building, illustrating in elevation the mechanism shown in Fig. 3.

Fig. 5 is a detail elevation illustrating certain additions to and modifications of the structure shown in Figs. 3 and 4,,whereby exhaust steam may be delivered to the heating system. 7

Referring first to Fig. 1, which illustrates a large building of the new set-back construction, it will be noted that this building has been divided graphically by dotted lines into eight separate blocks or sections A, B, C, l), E, F, G and H. The section D is not visible, but its location will be obvious from the drawings. It will be apparent that a building of this size is subject in different locations to a widely differing variety of temperature conditions. Certain portions of the building will be continuously shadedor protected by adjoining structures, whereas other portions will be constantly exposed to the sun or air currents. These conditions will vary at diilerent sides of the building, and at different heights. country, the heat requirements on the southern sides of buildings are not as great as on the northern exposures. The decreased crosssectional area and proportionately increased outside exposure of the upper portions of the building will usually increase the heat loss and require increased radiation from the heating system. If the steam or other heat ing medium were supplied to all portions of the building at the same temperature, it will be apparent that this temperature would have to be sufficient to meet the heat requirement of the coldest section of the building, and would, therefore, begreatly in excess of the heat requirements in other portions of the building. According to this invention, the building is divided into'a plurality of separate divisions or sections, and the heating medium is supplied to the group of radiators in each section at a temperature suii'icient to meet the average heat requirement of that section.

The steam or other heating Il'l0(lil111'l is supplied irom. a common source and the tenperature of the steam delivered to each section of the building is controlled by the subatmospheric pressure of the steam supplied to this section. More specifically, the pressure of the steam taken from the common source is reduced when it is delivered to each separate distributing system so'that the subatmospheric pressure of the steam supplied to that system will correspond to the steam temperature necessary to meet the average heating requirements in that section. In the example illustrated, the main lower section of the building has been divided into four corner blocks or divisions A, B, C and D. The next largest set-back has been divided into two sections E and ll. Presumptively one of these would be a northern ex- As a general rule in this posure and the other a southern exposure. The two upper setbacks have been divided vertically into two sections G and H. The example shown is merely illustrative, and each building would be divided into more or less sections, of varying size and location, according to the particular conditions presented by the location and construction of the building.

Referring now to Fig. 2, I will briefly describe a single unit of a differential vacuum steam heating system, such as is disclosed and claimed in my copending application Serial No. 171,616, hercinabove referred to. Steam "from any suitable generator is supplied through the reducing valve K and supply main L to the radiators Condensate and air are drawn out of the radiators through thermostatic traps N and through return main O to the accumulator tank P. The vacuum producing mechanism indicated genorally at It withdraws the condensates, vents the air, and forces the water back to the generator, or to a feed water heater or other receptacle, besides maintaining the desired vacuum throughout the system. The means indicated generally at S controls the vacuum producing mechanism so as to maintain a substantially fixed ditlerence in pressure between the supply and return mains, and the action mechanism is also under control at a float operated switch mechanism '1) which responds to the level of the accumulated liquid condensate in the tank P.

Steam passes from the boiler or other source of supply through pipe 1 and cut-off or gate valves 2, to and through the reducing valve K into the supply main L. The reducing valve K may be of the well known form embodying balanced cut-oil. valves whose movements to closed or open positions are governed by the enclosed pressure diaphragm and the balanced weights 4 and 5. The diaphragm 3 is subject on one side to the steam pressure in supply main L, by means of the pipe 6 connected at one end to the housing of the diaphragn'i and at the other end to the supply main at a point sullicienlly remote from the valve K to be uniniluenced by pressure disturbances in the vicinity of the valve. This reducing valve K differs from similar valves heretofore in use, in the fact that the balancing weights at and 5 are so proportioned and positioned that a desired sub-atmospheric pressure may beonaintained in the supply main L, while a higher pressure (either subatmospheric or super-atmospheric) exists in the supply pipe 1. By properly adjusting the weights 4 and 5 (or other equivalent spring or balancing devices which may be used), any desired degree of vacuum may be maintained in the supply pipe L. Preferably a pressure gauge 7 is provided to indicate this vacuum or sub-atmospheric pressure.

Instead of the manually adjusted reducing lill valve K, as shown in Fig; 2, an automatic temperature controlled valve might be substituted, as disclosed for example in my pending application Serial No. 171,616, hereinahove referred to.

The risers 8 lead from the supply main L to furnish steam to the several radiators M, two oi which are here shown by way of example, although it is to be understood that any desired nun'iher of radiators may be used. In a similar manner the risers 9, here shown, lead to radiators on a floor above those indicated in the drawings. Steam passes from the riser 8 through inlet valve 10 into the radiator M. This inlet valve will normally be 01 when the radiator is in seiwice to permit tree mssage of steam from the supply main to the radiator, but the valve may be closed when any individual radiator is not to be used for heating'purposes.

At the outlet of each radiator M is a thermostatically operated steam trap U, which normally retains the steam within the radiator, but permits the outflow of accumulated liquid condensate and air through pipe 11 to the return main 0. This thermostatic steam trap is preferably of the type embodying a valve which is moved toward or from its seat by the expansion or contraction of a fluidfilled thermostatic disc.

The liquid condensate and air flow downward by gravity, assisted by the suction of the vacuumproducing mechanism R, hereinafter described, through the return main 0 and suction strainer 12 into the accumulator tank P. The water of condensation and air accumulating in the supply main L is vented through the pipe 18, and float and thermostatic trap 14, and pipe 15 to the return main O, and is afterwards handled along with the condensates from the radiators.

The suction producing mechanism R, as here shown, comprises a tank 16 partially tilled with water, from the lower portion of which a pump 17 withdraws water through pipe 18 and forces this water upwardly through a jet eXhauster 19 back through pipe 26 into the upper portion of tank 16. This hurling water circuit produces a suction in the of ejector 19, which draws up the water and air from the lower portion of the accumulator tank T, through pipe 21, these gases and condensates being carried along with the water of the hurling circuit and dis charged into the tank 16., A one-way check valve 22 in pipe 21 prevents the return of these materials to the accumulator tank. The gases discharged into tank 16 are vented to the atmosphere through pipe 23, provided with check valve 24. The pipe 23 is here shown as discharging into a sewer connection at 25. A. second outlet from the centrifugal pump 17 leads through valve 26, pipe 27, check valve 29 and cut-oil valve 28 back to the steam generator, or to a feed water heater,

as in the installation hereinafter described. A float 30 in the tank 16 operates, when the of accumulated liquid in the tank 16 reached a certain height, through the i '1' l: and lever connections 31 to open the valve 1 l permits the pump 17 to force water out through pipe 27 and check valve 29.

The motor which drives the pump 17 is connected by wires 33 with the starter 3%, which under the separate and ind pendent control of two distinctswitch mechanisms 35 and Switch is controlled through lever mechanism 37 by a float positioned in the accumulator tank P. When a certain amount of liquid condo: to has gravitater through return main 0 1- 0 this tank, the flout 38 will be lifted sutiiciontly to close the switch 3 which results in starting the motor 32 and th vacuum producing mechanism commences to function to withdraw the condensates and air in tank P and discharge them into tank 16. Here the gases are vented thror 'h pipe 23, and when suiiicient water has accumulated, it is returned to the boiler or to the feed water heater in the manner already described.

Switch 36 is controlled by the differential pressure regulator ,S, which comprises a movahle diaphragm adapted in a well known manner to open or close the switch 36 through the lever connections 39. The diaphragm of ditferential. pressure regulator S is subject on its opposite sides to the pressure existing in the supply and return mains, one side being con nected through pipe 1-0 with the supply main L, and the other side thr ugh pipe 41 with the return main 0. Since both pipes 10 and 41 will become filled with liquid chndensate, they are initially filled with water and the vertical lengths of the two pipes must be of the same vertical height, as shown, in order to equalize the water head pressing on each side of the diaphragm of the pressiire regulator. When the ditl erence in pressure between the two mains falls below is certain minimum, switch will be closed, whereupon the mo tor 82 will be started and the pumping mechanism will operate to suck liquids and air from the tank P and hence from the return main 0. This will lower the pressure in the return main 0 and the pump will continue to operate until a desired maximum pressure differential is established between the return and supply mains, whereupon switch 36 will be opened to stop the motor 32.

In the normal operation of the system, as so fit! described, the reducing valve K is adjusted so as to maintain the desired degree of vacuum in the supply main L. As is well known, steam will be generated. at atmos pheric pressure at 212 F. Under higher pressures steam will i e generated at higher temperatures, and conversely under a vacuum, steam wil be generated at lower temperatures, the temperature of the steam dependill) ing upon the degree of vacuum existing in the system. 'lf his principle is utilized in this heating system so that by varying the sub-atmospheric pressure in the supply main L, the temperature of the steam delivered to the radiators M. is correspondingly varied so that steam at com paratively low temperatures may be maintained in the radiators when prevailing weather conditions necessitate only a mild radiation of heat from the radiators. Steam may be more economically generated at lower temperatures, and it is more el icient and economical to maintain a constant supply of steam at a comparatively low ten'iperaturo than an intermittent supply of steam at a higher temperature.

lVliile the degree of vacuum existing in the system may be varied from atmospheric pressure, or slightly above, to as low perhaps inches of vacuum, in order to obtain the desired heating efi'ect from the radiators, it is also desirable that a substantially constant and relatively small di'il crence in pressure he maintained between the supply and return sides of the radiators, this pressure diliferential being just suliicient to insure the proper circulation ofsteam and provide for withdrawing the condensates and air. Accordingly, the vacuum producing system is adj usted to operate to maintain this fixed pressure differential between the supply and return mains, but as hereinafter explained, in order to maintain this fixed differential, it Will also.

function to maintain the desired degree of vacuum throughout the system.

When starting the operation of this system, with a steam supply in the pipe 1, the pumping mechanism R is put into operation to create a suction in the system. At this time the system will be empty of steam and the thermostatic traps N will be open. There will be no substantial diiierence in pressure between the return and supply mains, and the suction created by the mechanism R will eX- tend throughout the system. When the degree of vacuum is attained, for which the reducing valve K is adjusted, this valve will open and permit steam from pipe 1 to pass into the supply main L, from which it is drawn into the radiators. Steam passing; through the traps N will close the valves in these traps until such time as sufficient condensate has accumulated to open these valves and permit its withdrawal. The pumping mechanism R will continue to operate until the sub-atmospheric pressure in return main i) which is now cut off from the supply main L by the closed trap N) has been lowered until the necessary pressure dil'lerential has been attained, whereupon the control mechanismS will operate the switch 36 to stop the motor 32. As steam condenses in the radiators M, the pressure in the radiators and.

is set, and this valve will open and admit nore steam to the supply main and radiators, thus keeping the radiators full of steam at the desired sub-atmospheric pressure. The thermostatic traps N will automatically open to permit the-accumulated condensate and air to pass out into the return main 0, and will again be closed when steam attempts to pass through these traps. This entry of air and condensate into the return main 0 will somewhat raise the pressure in this main so that the difference in pressure between the return main and supply main may fall below the necessary mininnun, whereupon the control lcvicc S will operate the switch 36 to start the motor 32, and the pumping mechanism R will begin tl unctioning at once to again reduce the pressure in the return main 0. The pumping mechanism R will only operate at such intervals as is necessary to maintain the pressure ditl'l'erential between the supply and return mains, or when the accumulation oi liquid in the accumulator tank 1 necessitates its removal to tank 16 and thence to the generator.

he object sought to be attained by this system is the substantially constant emission oi. heat from the radiators at a rate just sufiicientto replace the heat lost from the building. This is accomplished, not by turning the radiators on or oil at intervals, but by changing the temperature ot the steam maintained in the radiators, and this in turn is accomplished by varying the sub-atmos pheric pressure of this steam. This pressure variation is accoi'nplished, in the system here disclosed, by adjustment of the reducing valve K.

Having thus briefly explained the operation of one unit of the improved diff rential vacuum heating; system, I will now return to the expla at-ion oi. the multiple-unit system which forms the particular subject matter of the present invention. In general, it may be stated th t a system such as has just been briefly def ibed is utilized to indcpcnrb ently beat each oi the sections A to H inclusive of the building, as shown in Fig. 1.. Referring now to El p s. and l, at is shown the steam generating plant, consisting in this case of a group of boilers 42 to 4:7 inclusive. At X is shown the grouped or centralized control valves for the several branches of the system, and at Y is similarly grouped the pumping mechanisms for the several units. A Z is indicated the engineers room or control room, wherein the operator may observe the temperature conditions in the various portions of the building.

The several boilers 4:2 to 47 inclusive each feeds through a pipe 48 and valve 49 into the high pressure header 50. Steam is led from high pressure header 50 through reducing valves 51 and pipes 52 to the lower pres sure headers 53 and 54. Steam is supplied through the several pipes 1 leading from headers 53 and 54 to the group of reducing valves K to K inclusive to the supply pipes L to L inclusive of the eight distinct branch heating systems which supply heat to the respective sections A to H of the building, as indicated in Fig. 1. At an adjacent location, the return pipes O to O" of these re spective branch heating systems lead back to the accumulator tanks P to P respectively. The condensate delivery pipes 27 of the several branch systems all feed into a common header pipe 55, leading through check valve 56 to the feed water heater indicated diagrammatically at 57. A pair of similar boiler feed pumps 58 and 59 connected in multiple so that either 'one or both may be used, serve to pump water from the feed Water heater 57 through pipe 60 and header 61 back into the several boilers 42 to 47 inclusive. By means of the several valves 62 and feed pipes 63, the water may be fed selectively from header 6linto any desired boiler or boilers.-

Steam may flow from the low pressure header 53 through pipe 64 and the auxiliary reducing valve K (similar in all respects to any one'ot the reducing valves K to K into the by-pass pipe 65 positioned transversely oi the several supply pipes L to L inclusive. From the by-pass pipe 65, branch pipes 66 lead through cut-efi valves 67 into the respective supply pipes L to L This reducing valve K and by-pass 65 serve as an emergency control valve which may be substituted for any one of the main reducing valves K to K respectively. In a similar manner, branch return pipes 68 lead through cut-off valves 69into the by-pass pipe 70 which feeds into an auxiliary accumulator tank P. The auxiliary pumping unit R feeds back into the header 55 similarly to the main pumping units R to R inclusive. By suitably manipulating the cut-off valves 28 and 69, the auxiliary pumping unit may be substituted for any one of the units R to R In this way, any one of the pumping units may be withdrawn from service when repairs are necessary, without incapacitating the corresponding branch heating system.

In a certain key-room 71 (see Fig. 1) in each of the sections A to H inclusive, which rooms are selected to give the average temperature conditions in each respective section, are located therntiometers or thermostats which respectively actuate certain indicating instruments 72 in the instrument room Z. By means of these indicators 72, the engineer or operator can see at anytime the temperature con ditions existing in each of the several sections of the building and can regulate the reducing valves K accordingly to bring the temperatures to any desired normal. For

example, let us suppose that it is desired to.

maintain a temperature of 70 F. throughout the building, but the engineer notes that the indicator 72 corresponding to the section Gr indicates that a temperature lower than this, for example, 65, prevails in that section of the building. Assuming that the re ducing valve K controls the branch heating system leading to section G, the engineer will adjust this valve so as to increase the pressure (or decrease the vacuum) of the steam supplied to this branch heating system. This will increase the temperature of the steam delivered to this respective section of the building and will bring the temperature back to normal. On the other hand, let us suppose that one of the indicators shows that the temperature in building section F has become too high, for example F. Assuming that the reducing valve K controls this branch heating system, the engineer will adjust this valve so as to decrease the pres sure (that is increase the vacuum) in the sup ply pipe L leading to this section of the building. This will decrease the temperature of the steam delivered to this branch heating system, and the resulting decreased radiation from the radiators in this section of the building will bring the temperature back to normal. If desired, pressure indicators 73 may also be located in the instrument room Z showing the respective sub-atmospheric pressures existing in the several branch heating systems. Other pressure indicators will also be located either in the instrument room or adjacent the several pumping units to shoiv that the proper pressure differential is being maintained between the supply and return pipes of each branch system.

The distinct advantage of this system resides in the fact that steam of various temperatures can be simultanenously furnished to dillerent parts of the same building having different exposures and difierent heat losses. The amount of heat Waste is minimized through the prevention of overheating an unexposed section in order to keep the exposed section fully heated. lVith this system it is possible to maintain the entire building at a substantially uniform temperature without continually turning on and oil the radiators in those portions of the building where less heat is required. The centralized system of control permits the entire system to be regulated by a single operator who is always cognizant oi the temperature conditions prevailing in any part of the building.

lVhile in the example here illustrated, we have shown a steam generator capable oi de veloping high pressure steam, this steam pressure being brought down by reducing valves before it is delivered to the low-pressure headers 53 and 54, it is not at all essential to the operation of this system that high pressure steam be developed. The pressure in the boiler need not exceed the pressure required to heat the most exposed portion of the building, and this boiler pressure may even be sub-atmospheric. However, in a building of this size, high pressure steam is usually required for other purposes, such as supplying engines and other power developing apparatus, and for that reason, a high pressure system has been disclosed. It only a low pressure is developed in the boilers, the feed water heater 57 and boiler teed pumps 58 and 59 may be eliminated, and the condensate discharged directly to the boilers by the several pumping units R to R respectively.

It is not unusual in large buildings in most cities to have central steam supplied from an outside source instead of by a boiler plant in the building. In such an installation the steam would be delivered to the low pressure headers 53 and 54: through suitable reducing valves in a similar manner to that already described. In such a system, that portion of the apparatus which is utilized to deliver the condensate back to the boiler could be eliminated.

In Fig. 5 is illustrated a modification whereby exhaust steam from engines or other high pressure apparatus may be utilized. A

. header 74 positioned parallel with the low pressure header 54 is connected through branch pipes 75 in which are located reducing valves 76 and cut-oil? valves 77, with the several supply mains L. The exhaust steam header 74 may take the place of the by-pass pipe 65,already described,or may be arranged in parallel therewith. The reducing valves 76 may be similar in all respects to the reducing valves K, already described, and by suit ably adjusting these valves and the cut-01f valve 77, the exhaust steam may be fed into any or all of the supply pipes L, either simultaneously with or as a substitute for the steam supplied direct from the boilers through the reducing valves K. It will be noted that this exhaust steam is delivered directly into the vacuum mains L, thus making possible a reducing of the pressure in the exhaust pipes and adding materially to the power of the engines.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

1. The method of heating by steam which consists in supplying steam to a plurality of separate distributing systems withdrawing condensate from said systems without permitting escape of steam therefrom, and independently adjusting the pressure of the steam delivered to each separate system in accordance with the heat output desired in the space heated by that system.

2. The method of heating by steam which consists in supplying steam to a plurality of separate distributing systems, and independently adjusting the pressure of the steam delivered to each separate system in accordance with the heat output desired in the space heated by that system, and separately maintaining a pressure differential between the supply and return sides of each system sullicient to insure the flow of steam through the system.

3. The method of heating by steam which consists in supplying steam from the same source to a plurality of separate distributing systems, and independently adjusting the pressure of the steam delivered to each separate system in accordance with the heat output desired in the space heated by that system, separately maintaining a pressure diilerential between the supply and return sides of each system sufficient to insure the flow of steam through the system, and delivering the condensate from the several systems back to the common source of supply.

4. The method or heating by steam which consists in supplying at sub-atmospheric pressures steam to a plurality of separate distributing systems, and independently varying the sub-atmospheric pressure or the steam delivered to each system in accordance with the heat output desired in the particular space hea ed by that system.

5. The method of heating by steam which consists in supplying at sub-atmospheric pressures steam to a plurality of separate distributing systems, independently varying the sub-atmospheric pressure of the steam delivered to each system in accordance with the heat output desired in the particular space heated by that system and separately maintaining a pressure diiierential between the supply and return sides of each system suilicient to insure the flow of steam through the system.

6. The method of heating by steam which consists in supplying at sub-atmospheric pressures steam from the same source of supply to a plurality of separate distributing systems, independently varying the. subatmospheric pressure of the steam delivered to each svstem in accordance with the heat output dcsii'ed in the particular space heated by that system, separately maintaining a pressure diilerential between the supply and return sides of each system suiiicicnt to insure the flow or" steam through the system, and delivering condensate from the several systems back to the common source of supply.

7. The method of heating by stcaun which consists in simultaneously condensingsteam under sub-atmosphcric pressures in u plurah ity of separate groups of condensing spaces at difi'erent locations in a building, and regulating the heat output in accordance with the requirements at each location by separatelv controlling the sub-atmospheric pressure oi the steam in each group of condensing spaces.

8. The method of hea'tig by steam which consists in simultaneously supplying steam at different sub-atmospheric pressures to different portions of the building to be heated in accordance With the heat output desired at these difierent locations.

9. The method of heating by steam which consists in providing plurality of separated groups of condensing spaces at different locations in a building, Withdrawing no1rcondensable gases and condensate from these spaces Without permitting the escape oil steam therefrom, and simultaneously and separately controlling the amount of steam introduced into each of these groups ot condensing spaces in accordance With the heat output desired at each of these locations.

10. The method of heating by steam which consists in providing a plurality of separated condensing spaces at different locations in a building, Withdrawing non-condonsable gases and condensate from these spaces Without permitting the escape of steam therefrom, and separately controlling the supplyot steam to each of the spaces so that the steam in each space is maintained at a desired sub-atmospheric pressure, diil'erent sub-atmospheric pressures being simultaneously maintained in the diilerent spaces in accordance With the heat output desired at each location.

11. The method or heating by steam which consists in providing a plurality of separated groups of condensing spaces at different locations in a building, each group of condrising spaces having separate supply and discharge passages, ellecting the Withdrawal {from each of the spaces of non-condensable gases and condensate, as formed, While retaining the steam therein, by maintaining the pressure in the discharge passage lower, by a relatively constant difference sufficient to keep up circulation, than the pressure in the condensin spaces, and separately limiting the inflow or steam through each of the supply passages to Vary the temperature in each group of condensing spaces in accordance with the heat output desired at that particular location.

12. The method of generating and utilizing steam for heating which consists in gen erating the steam in one space and condensing the steam in a plurality of separated groups of condensing spaces at different locations in a building, Withdrawing non-condensable gases and condensate, as formed, from each oi the condensing spaces, Without permitting the escape of steam therefrom, ano separately restricting the flow of steam from the generating space to each of the groups of condensing spaces in accordance With the heat output desired at each location.

13. The method of generating and utilizing steam tor heating Which consists in generating the steam in one space and condensing the steam in plurality of separated groups o'ficondensingspaces at ditl'erent locations in a building, withdrawing non-condensable gases and condensate, as formed, from each of the condensing spaces, without permitting the es cape of steam therefrom, separately restricting the flow of steam from the generating space to each of the groups of condensing spaces in ace rdance with the heat output desired at each location, and returning the con densate from each condensing space to the generating space.

CLAYTON A. DUNHAM. 

